The present invention relates to workpiece holding devices and particularly, to high tolerance chucks for mounting a workpiece to a machine tool. More particularly, the present invention relates to a collet for a machine-tool chuck that is actuated by other components of the chuck to move the collet into gripping engagement with the workpiece.
A collet is a ring, band, or collar that is included as one of the components in a machine-tool chuck. The collet is the component of the chuck that grips and releases a workpiece. Chucks also include mechanisms that retain the collet in position and mechanisms that engage the collet to move the collet into gripping engagement with the workpiece to be machined by the machine tool. If the bore of a workpiece is to be gripped, the chuck will be configured to expand the collet radially outwardly into engagement with the bore of the workpiece and if the outside diameter of the workpiece is to be gripped, the chuck will be configured to contract the collet radially inwardly into engagement with the outside diameter of the workpiece. Some chucks include more than one collet and are configured to grip both the bore and outside diameter of the workpiece.
According to the present invention, a collet includes a flexible circular collet body having an outer circular periphery and an inner circular periphery. The flexible circular collet body is formed to include an opening extending between the outer and inner circular peripheries. One of the circular peripheries is formed to includes a workpiece-grip surface and the other of the circular peripheries is formed to include a tapered cam surface adapted to be engaged to flex the flexible circular collet body circularly so that the workpiece-grip surface engages a workpiece to be held by the collet. The tapered cam surface is formed to include a plurality of circumferentially spaced slots. Each slot includes an open end and terminates at an inner end between the inner and outer circular peripheries.
In preferred embodiments, if the collet is designed to grip the bore of a workpiece, the workpiece-grip surface is formed on the outer circular periphery of the collet body and the tapered cam surface is formed on the inner circular periphery of the collet body. In addition, each of the plurality of slots has the respective open end at the inner circular periphery and each slot extends outwardly toward the outer circular periphery. If the collet is designed to grip the outside diameter of the workpiece, the workpiece-grip surface is formed on the inner circular periphery of the collet body and the tapered cam surface is formed on the outer circular periphery of the collet body. In addition, each of the plurality of slots has the respective open end at the outer circular periphery and each slot extends inwardly toward the inner circular periphery.
The collet of the present invention is usable in a variety of different machine-tool chucks. Each of the chucks in which the collet is included as a component also includes an actuator member having a tapered surface that is complementary to the tapered cam surface formed in the collet. Each of the chucks with which the collet of the present invention is used also includes a chuck body which supports the actuator member for axial sliding movement.
During the manufacturing process of the collet and chuck, the collet is machined and matched with a particular actuator member and the tapered surfaces of each of these parts may be subjected to additional machining operations, if necessary, to further optimize the ability of the respective tapered surfaces to mate with one another. In addition, before the completion of each collet, a preassembly grind operation is performed on the workpiece-grip surface of the collet. The preassembly grind operation involves assembling the chuck together, actuating the actuator member, and then grinding the workpiece-grip surface with the actuator member actuated. Grinding the workpiece-grip surface in this manner compensates for any eccentricities or out-of-roundness conditions in the "total system." The rotational position of the collet during the preassembly grind operation is marked and an anti-rotation device is included in the chuck so that, after final assembly, the collet occupies the same radial position related to the other chuck components that was occupied by the collet during the preassembly grind operation.
Additional features of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.